1. Field of the Invention
The present invention relates to a projection device, a projection control method, and a storage medium.
2. Description of the Related Art
In Jpn. Pat. Appln. KOKAI Publication No. 2009-265120, there is proposed a technique for providing a projection-type display device which can realize a high contrast in a display screen. In this technique, two light modulation elements are provided on a projection optical path, and a product of the contrasts of these two light modulation elements is set as a synthetic contrast.
There have been proposed various techniques including the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2009-265120, which aim at realizing a high contrast by adopting a complex configuration, for example, by using a diaphragm mechanism or a shutter mechanism, and two light modulation element mechanisms, on an optical path of a projection system.
In the meantime, in recent years, a projector device has been commercialized, which employs a semiconductor light-emitting element, such as a light-emitting diode (LED) or a semiconductor laser (LD), as a light source.
In the projector device using this kind of semiconductor light-emitting element as the light source, the element itself of the light source is temporarily turned off in synchronism with a video timing when the entire screen becomes all black during a projection operation. Thereby, the occurrence of so-called “black-floating” due to leak light, etc. in the display element is avoided, and a much higher contrast can be obtained.
When the elements of the light source were turned off at the same time in synchronism with a video timing when the entire screen becomes all black, as described above, completely black video appears instantaneously in a projected image from the state in which the light source had been turned on, and there may be a case in which a user feels an abrupt change and some unnaturalness as an expression of projected video.
Thus, when video images in which the entire screen is all black continue, such a driving method is thinkable that the emission brightnesses of the elements of the light source are gradually lowered by setting a fixed time width of, for example, about one second.
However, for example, when three kinds of LEDs (light-emitting diodes) with emission light colors of R (red), G (green) and B (blue) are used as the semiconductor light-emitting elements that are used for the light source, the light emission physical characteristics, such as forward-directional drop voltages, vary from color to color, to be exact, from element to element of LEDs to be used. It is thus difficult to turn off the LEDs of all colors exactly at the same time, during the process of gradually lowering the emission brightnesses of the respective colors.
As a result, the emission light color of an LED, the turn-off of which was delayed, is perceived by the user as a single primary color or a complementary color due to color mixture, and the emission light color is recognized as an unnatural projection image immediately before the entire screen becomes all black.
Accordingly, it is an object of the invention to provide a projection device which makes possible a more natural, smooth transition to video in which an entire screen is all black, a projection control method and a program.